In most IDEs, you normally type some code, press <C-Space> for a completion popup menu, type some more characters to select the menu item you want, then hit <Enter> to insert that completion into the code. With Vim's initial popup menu settings, the behavior of the popup menu is a little less pleasant (for some people).

The first step to "improve" the menu behavior is to execute this command:

:set completeopt=longest,menuone

The above command will change the 'completeopt' option so that Vim's popup menu doesn't select the first completion item, but rather just inserts the longest common text of all matches; and the menu will come up even if there's only one match. (The longest setting is responsible for the former effect and the menuone is responsible for the latter.)

The next enhancement is the following mapping:

:inoremap <expr> <CR> pumvisible() ? "\<C-y>" : "\<C-g>u\<CR>"

The above mapping will change the behavior of the <Enter> key when the popup menu is visible. In that case the Enter key will simply select the highlighted menu item, just as <C-Y> does.

In the above mappings, the first will make <C-N> work the way it normally does; however, when the menu appears, the <Down> key will be simulated. What this accomplishes is it keeps a menu item always highlighted. This way you can keep typing characters to narrow the matches, and the nearest match will be selected so that you can hit Enter at any time to insert it. In the above mappings, the second one is a little more exotic: it simulates <C-X><C-O> to bring up the omni completion menu, then it simulates <C-N><C-P> to remove the longest common text, and finally it simulates <Down> again to keep a match highlighted.

Here is a hacky example of a set of mappings that first close any popups that are open which means you can seamlessly switch between omni and user completions. Then they try the omni or user complete function. If the menu is visible they use the above trick to keep the text you typed and select the first.

I don't know. Tip 1228 doesn't explain what their mappings do at all, and there are a lot more of them. This tip tells what's going on, although admittedly it does not tell how it works (which I would like).

Works for me! What version of Vim do you have? It looks like your Vim is ignoring the <expr> tag and using the mapping literally instead of evaluating it as an expression first. :map-expressions are a feature introduced in Vim 7, and I do not see any compile-time option for removing them. --Fritzophrenic 20:05, February 22, 2011 (UTC)

Again, works fine for me, and I've had something similar in my setup since Vim 7.1. Do you use Vim in "easy mode" or with 'insertmode' set? Maybe you have a "tiny" build or similar? I can't really think of any reasons it would not work unless you entered the mapping wrong. Try contacting #vim on Freenode or the vim_use mailing list. See Asking questions for details. --Fritzophrenic 03:10, March 17, 2011 (UTC)

For me everything works until I install "SuperTab continued"; that's when I get the error you describe. Unfortunately, I don't have a solution yet. Will update if/when I do.

When using SuperTab w/ these mappings use this to avoid the mentioned troubles:

let g:SuperTabCrMapping = 0

--Mklein, January 25, 2012

Found a fix, just change <CR> into <C-CR> and magically enter will start working again without holding ctrl. I don't know that works but it is working for me at least on VIM 7.3

Pencilcheck December 26, 2012

If you like the part of the tip where <C-n> automatically selects the first entry by simulating <Down>, you can add the same thing for simulating <Up> when searching backwards with <C-p>:

Where does vim takes the commands from? Is there a text file for each language from where it reads the list of commands to show in the auto-completion pop-up.

There are many different ways Vim can do completion. See :help ins-completion for details. What you are describing sounds most like "dictionary completion", see :help compl-dictionary and :help 'dictionary'.

It would be really nice if the above functionality for omni-complete would fall back on C-N if it can't find anything. Does anyone know a simple way to do this? I am still not very good at vim-script.

You might be able to make a mapping that does <C-X><C-O> then checks if the popup is visible using the pumvisible() function, if you have "menuone" in your 'completeoptions' setting. Then if the popup isn't visible end the current completion and use <C-N>. I'm not sure how well it would work, though; and it's pretty complicated. --Fritzophrenic 14:47, June 8, 2012 (UTC)